Methods and conveyor systems of this type are known in practice, e.g., in association with packaging machines and packaging plants. The use of such conveyor systems often necessitates the transfer of articles (in the case of packaging machines: e.g., packages) from an irregular mode of arrangement on a first conveyor means to a regular, equidistant mode of arrangement on a second conveyor means. Likewise, it may become necessary to transfer articles from a regular mode of arrangement with a first mutual distance on the first conveyor means to a regular mode of arrangement with a second, different mutual distance on the second conveyor means. In this way, the articles on the second conveyor means can be grouped, arranged and further transported at a predetermined distance from one another.
In this context it is important in many cases to avoid a relative movement between the two conveyor means during transfer of an article from the first to the second conveyor means, i.e., the two conveyor means have to move at the same speed during a so-called “synchronous phase”. Otherwise, uncontrollable slip may occur or the articles may cant, and equidistant grouping would consequently be impossible. In addition, abrupt acceleration or abrupt deceleration might occur during transfer from one conveyor means to the other. This may, if the packages conveyed contain liquid products, e.g., lead to spilling over and thus to a contamination of the conveyor system.
FIG. 5 exemplarily shows the curve of a speed profile of a first and of a second conveyor means in a conventional conveyor system. The conveyed articles are here transferred from a first conveyor means to a second conveyor means. The speed profile of the first conveyor means is shown in the form of a solid line, and the speed profile of the second conveyor means is shown in the form of a broken line. The speed profiles of the two conveyor means recur periodically. A period or work cycle starts with a stationary phase in which both conveyor means are standing still. At the moment in time t1, the first conveyor means, which has to travel a longer distance than the second conveyor means until a synchronous phase begins, starts moving in an accelerated mode. This acceleration takes place until a maximum speed vmax has been reached. At a later moment in time t2, also the second conveyor means starts moving. Precisely at the moment at which the second conveyor means reaches the maximum speed vmax, i.e., at the moment in time t3, the synchronous phase, in which the two conveyor means move at a constant and common speed vmax, begins. The synchronous phase is timed such that, during said synchronous phase, the articles (e.g., packages) are transferred from the first conveyor means to the second conveyor means.
At the moment in time t4, the synchronous phase ends. First, only the second conveyor means is decelerated, since the first conveyor means still has to travel another distance and therefore maintains its speed vmax for the time being. Only after a certain period of time, also the first conveyor means is decelerated. At the moment in time t5, the second conveyor means comes to rest, and at a later moment in time t6 also the first conveyor means. The moment in time t6 thus functionally corresponds to the moment in time t0, i.e., a new cycle starts at the moment in time t6.
The speed profiles shown in FIG. 5 are determined by the boundary conditions that are predetermined by the two conveyor means. For example, the speed of the two conveyor means must not exceed a specific maximum speed, since the conveyor means are normally designed only for a certain maximum speed, or since the speed at which the articles are conveyed must not exceed a certain maximum speed. If the article in question is e.g., salad in a package, the salad, if conveyed at an excessively high speed, may be blown over the edge of the package. In addition, a specific acceleration or deceleration must not be exceeded, since otherwise the conveyor means, its drive, or the article conveyed by the conveyor means may have applied thereto excessive loads or the friction required between the conveyor means and the article for the purpose of transport may decrease excessively or a liquid content of the article may spill over. Moreover, the two conveyor means have to travel certain distances so that they will be able to transfer the articles at specific moments in time and group them on the second conveyor means at predetermined distances from one another. In the time-speed diagram according to FIG. 5 the distance to be travelled is obtained as an integral under the respective speed profile.
In the so-called “acceleration phase” between the moments in time t1 and t3, i.e., from the beginning of the acceleration of the first conveyor means to the beginning of the synchronous phase, the integral under the speed profile of the first conveyor means and thus the distance travelled by said first conveyor means is larger than the integral under the speed profile of the second conveyor means. The maximum acceleration of the two conveyor means determines how steep the maximum gradient of the speed profile curve can be. Starting from the respective distance to be travelled and the desired moment in time t3 at which the synchronous phase should begin, the starting points t1 and t2 for the acceleration of the respective conveyor means are obtained. The same considerations also apply analogously to the deceleration phase between the moments in time t4 and t6. Also in this case the first conveyor means has to travel a longer distance than the second conveyor means in the example shown. The integral under the speed profile of the first conveyor means must be correspondingly larger. This is accomplished in that the first conveyor means maintains, after the end of the synchronous phase at the moment in time t4, its maximum speed vmax longer than the second conveyor means.